1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to a secondary battery having an improved coupling structure of a resin molding part molded on a bare cell.
2. Description of the Prior Art
As video cameras, cellular phones, portable computers and other electronic devices have become more sophisticated, much research has been conducted on secondary batteries used to power such devices. A secondary battery may be, for example, a nickel-cadmium battery, a nickel-hydrogen battery, a nickel-zinc battery, a lithium secondary battery and other similar batteries. Among these batteries, lithium secondary batteries can be recharged and also can be compact yet have a high capacity. Lithium secondary batteries are widely used in the field of high-tech electronic equipment because of their high operating voltage and high energy density per weight.
A lithium secondary battery may include a bare cell formed by inserting an electrode assembly having cathode plates, anode plates and separators into a metal can, injecting an electrolyte into the can, and sealing the can. The bare cell formed as described above typically has an electrode terminal insulated from the can. The electrode terminal forms one electrode of the lithium secondary battery, and the can itself forms the other electrode of the lithium secondary battery. Accordingly, the cathode plates and the anode plates of the electrode assembly may be connected with either the can and the electrode terminal.
By connecting the bare cell with safety devices, for example, a protecting circuit module (PCM) including a secondary protective element, such as a bimetal or a positive temperature coefficient (PTC), and a protective circuit board and inserting in a battery pack or molding using resin, the lithium secondary battery is formed. The safety devices of the lithium secondary battery are connected with the cathode and the anode, preventing the risk of explosion of the battery by blocking the electric current when the voltage of the battery is rapidly increased due to, for example, the increase in battery temperature or over-charging/over-discharging.
A conventional general lithium secondary battery includes a bare cell and a protective circuit board on the upper part of the bare cell. The lithium secondary battery also includes a secondary protective element arranged on the upper part of the bare cell. The secondary protective element may be formed on the side or the top of the bare cell depending on the construction of the lithium secondary battery.
The bare cell includes a can, an electrode assembly and a cap assembly. The can is a metal container, the top of which is opened, having an approximately hexahedronal shape. The electrode assembly includes cathode plates, separators and anode plates which are all housed in the can along with electrolyte. After the electrode assembly is inserted through an opened top opening of the can, the top opening is sealed by the cap assembly.
Lithium secondary battery with a resin, the cap assembly, the secondary protective element and the protective circuit board can be protected. The can and a resin molding part form the exterior of the lithium secondary battery, and the electrode terminals are exposed on the upper part of the resin molding part.
However, when a conventional lithium secondary battery is assembled, the material of the resin molding part fixedly coupling the battery protection components with the bare cell is different from the material of the bare cell and the contact area of the resin molding part is narrow. Accordingly, the adhesive strength between the components is low, and the resin molding part cannot be positioned in its molding state without twisting of the resin molding part occurring. As such, lead plates are typically expanded or the reinforcing structure of the secondary protective element is formed separately, resulting in higher manufacturing costs.